Method and apparatus for stretch-bend leveling metal strip

ABSTRACT

The invention relates to a method and to a device for the stretch-bend leveling of a metal strip (B), wherein the metal strip (B) is alternately bent around stretching rollers ( 1 - 5 ) under a tensile stress and the degree of stretching is thus increased, wherein one or more stretching rollers ( 1 - 5 ) are provided with a non-metal coating. The method and the device are characterized in that one or more stretching rollers are provided with a coating ( 8 ) of plastic.

The invention relates to a method of stretch-bend leveling metal strip where the metal strip is alternately bent around stretching rollers (of a stretch bending frame) thereby creating the stretching rate and/or increasing it, such that one or more stretching rollers made of metal, for example, are provided with a nonmetallic coating (on the circumference) and consequently are provided with a jacket. In doing so the strip usually passes through an inlet tension roller set to establish the tension and an outlet tension roller set to release the tension, such that the strip is alternately bent around the stretching rollers between the inlet tension roller set and the outlet tension roller set, thereby creating and/or increasing the stretching rate.

With such a stretch-bend leveling method, uneven metal strips can be leveled, and consequently, nonplanarity can be eliminated. Unevenness refers to strip waviness and/or strip warping, for example, which is/are the result of differences in the length of the strip fibers in the plane of the strip. Within the context of the present invention, such unevenness is to be differentiated from strip warping in the longitudinal and/or transverse direction(s), which results from bending torques in the strip, for example, when elastic-plastic deformation of the strip occurs in bending around deflecting rollers and when elastic-plastic deformation of the strip occurs in winding. Longitudinal warping is also referred to as coil set, while transverse warping is known as cross bow.

Following stretch-bend leveling, the uneven strip is bent around rollers of a small enough diameter (alternately) with a tensile stress that is below the limit of elasticity RE and/or the technical elasticity limit RP0.01 of the strip material, so that elastic-plastic deformation is created in the strip by superimposing the bending on the tensile stress. The strip is elongated with plastic deformation, so that the level of plastic elongation is referred to as the stretching rate. In plastic elongation, strip fibers that were originally short are lengthened to a relatively great extent. In the ideal case, all the strip fibers are of the same length after stretch-bend leveling, so that basically an ideally leveled strip that is free of waviness or strip curl is formed.

In practice, such a stretch-bend leveling method is usually carried out with a stretch-bend leveling apparatus having at least one stretch bending frame. Such a stretch bending frame will in practice often have three or five stretching rollers.

Within the scope of the present invention, the term “stretching rollers” preferably refers to stretching rollers supported individually (on backing rollers), and optionally one or more stretching rollers may be individually adjustable. To this extent, such a stretch-bending frame with its stretching rollers is to be differentiated from a multiroller leveling unit of the type that is also known per se but usually has one fixed cassette and one adjustable cassette, each having a plurality of leveling rollers and backing rollers. The leveling rollers are usually coupled to one another in a friction-drive manner by the backing rollers in the respective cassette within such a multiroller leveling unit, i.e. all the leveling rollers (of a cassette) rotate at the same speed. In such a multiroller leveling unit, residual warping is usually eliminated in such a way that the strip is not usually under a tensile stress or is under just a slight strip tension in the multiroller leveling unit. No “global” stretching rate is produced.

Stretch-bend leveling according to the invention is therefore to be differentiated from elimination of residual strip warping in a multiroller leveling unit (with little or no strip tension and without creating any significant stretching rate). A stretching rate of at least 0.2% is usually produced with the stretching rollers and/or with the stretch-bend leveling frame. The strip is usually under a tensile stress of at least 15%, preferably at least 20%, of the yield strength of the metal strip.

It should also be pointed out that, in practice, the metal strip will not always be completely clean on entering the stretch-bend leveling installation and/or the stretch-bend frame. The surface of the strip is often soiled or coated with a film of residual rolling oil. Furthermore, the metal strips often processed in practice are aluminum strips that have been provided with a surface oxide layer, but during extreme bending around the stretching rollers in stretch-bend leveling, this oxide layer ruptures, thereby releasing oxide particles from the surface of the strip. In practice, the stretching rollers in stretch-bend leveling are usually provided with a metal surface, such as hardened steel. Particles of dirt and/or oxide may adhere to these roller surfaces, on which they may gradually build up, resulting in vibrations, which in turn cause unwanted chatter marks on the strip.

To prevent dirt and/or oxide particles from adhering to the rollers and the problems associated therewith, it is customary in practice to operate the stretch-bend leveling process as a wet operation. The strip and possibly also the stretching rollers and backing rollers are sprayed with a spray medium or treated in some other way at the inlet end. The problematical particles are washed off in this way, and a buildup of particles on the rollers is prevented. Water-based media are used in practice here as the spray media. One disadvantage is that the strip here must be completely cleaned and dried before winding because otherwise the residual moisture would result in corrosion damage in the wound coil. Alternatively, solvent-based spray media, for example kerosene-based media, may be used. Evaporation of the solvent here is a disadvantage, so that suction ventilation must be provided, and it may be necessary to scrub the exhaust air. Furthermore, fire-prevention equipment must be provided because such solvent vapors are flammable.

Another disadvantage of using spray media is that a strip with the residual moisture may have a tendency to slip on the tension rollers of the outlet tension roller set. As a result, the tension rollers can only be designed with lower transmission factors.

Alternatively, EP 0 276 614 proposes that the stretching rollers in the stretch-bend leveling process should be provided with a jacket of a ceramic material, namely with a composition that not only has an adequate hardness but also has a very low wettability with regard to liquids in order to prevent metal strip jacket particles and oxide particles from adhering to the roller. Production of the ceramic layer may be based on aluminum oxide, for example. In practice, however, implementation of such stretch-bending rollers with a ceramic jacket has posed substantial problems.

Against this background, the object of the present invention is to create a method and an apparatus for stretch-bend leveling metal strip of the type described in the introduction, which will make it possible to manage the process as a dry operation in a structurally simple manner.

To achieve this object, the present invention teaches that the stretch rollers should be provided with a jacket of plastic in a generic method and with an apparatus for stretch-bend leveling metal strip. Within the scope of the invention, the term “plastic” refers to a polymer material, in particular a synthetic polymer material including rubber. It is preferably a jacket of polyurethane or a comparable plastic. Alternatively, for example, a jacket of polyamide may also be used.

Plastic jackets are usually already known in practice in conjunction with tension rollers and deflecting rollers used to optimize friction, for example, and thus improve the transmission factors, or to protect the strip surfaces. For stretch rollers in stretch-bend leveling, in which the strip is under a tensile stress of usually at least 15% of the yield strength of the metal strip, preferably at least 20%, and in which a stretching rate of at least 0.2% is created by using the stretching rollers, the use of such plastic jackets, for example polyurethane jackets, has not previously been considered. It has now surprisingly been found that instead of the usual stretching rollers made of steel, stretching rollers with a polyurethane jacket, for example, can be used for stretch-bend leveling of aluminum strips, for example. Consequently, such stretching rollers preferably consist of a roller core made of metal, for example, steel, and a jacket of plastic, for example, polyurethane. With such a jacket, the stretch-bend leveling process can be carried out as a dry process. It has surprisingly been found that although the stretching rollers initially become soiled, the degree of soiling stabilizes at a level that allows dry operation without resulting in any strip surface damage. It is thus possible to eliminate the spray systems that are used in practice, so that the associated disadvantages are avoided. In contrast with the ceramic jackets proposed in the prior art, plastic jackets, in particular polyurethane jackets, can be produced easily and inexpensively, and it has surprisingly been found that the angle of wrap around the stretching rollers can be set to be low enough that the maximum allowed linear load for the jacket is not exceeded, depending on the strip tension. Although there have been some fears in conjunction with polyurethane surfaces, namely that the segmented backing rollers or intermediate rollers, for example, might produce impressions on the polyurethane surface have not been confirmed. Despite a very high required strip tension for the desired stretching rate, the resulting linear load on the stretching roller is low enough on the whole and is less than the maximum load allowed for the polyurethane jacket. In addition, a plastic jacket, for example, a polyurethane jacket, also has a certain vibration-damping effect, so that vibrations and chatter marks are minimized or prevented. Soiling of the backing rollers, which usually occurs in practice, is not observed in dry operation.

It is therefore possible on the whole to satisfactorily process metal strips in a dry operation and without any damage to the surface.

Use of a plastic jacket in a multiroller leveling unit is described in the prior art according to JP63-199023 and JP63-199024. In such a “roll leveler,” the metal strip is usually not under little or no strip tension, and there is also no noticeable stretching rate, so that there are only very low loads on the rollers and the jackets. Protection of the metal strip by the plastic jacket is the main concern, so that damage to the strip should be prevented. Against this background, the invention is based on a different idea. Within the scope of the present invention, a jacket with a Shore A hardness of at least 90 is preferably used. The jacket may be at least 1 mm thick, preferably at least 3 mm thick. It is therefore possible to use a 1 mm thickness to 10 mm thickness, for example preferably 3 mm to 7 mm. The stretch rollers preferably have a diameter of 25 mm to 100 mm, for example, 35 mm to 70 mm. The diameter refers to the core, i.e. these values do not include the plastic jacket.

The stretching rollers are each supported individually in stretch-bend leveling and/or in a stretch-bend leveling frame, i.e. they can each be supported individually on at least two backing rollers and optionally a plurality of intermediate rollers. In contrast with a multiroller leveling unit, the individual stretching rollers (for example below or above the strip) are not connected to one another in a friction-drive manner by the backing rollers but instead are supported individually, so that they can rotate at different speeds. Preferably one or more stretching rollers can be adjusted individually. For example, there is the possibility of all stretching rollers being adjustable individually. Usually, however, it is also possible in the case of a plurality of stretching rollers to adjust only the lower stretching rollers with respect to the upper stretching rollers, or conversely, to adjust the upper stretching rollers with respect to the lower stretching rollers. Preferably, however, the angle of wrap on each individual stretching roller is adjustable individually and independently of the others.

Coating the stretching rollers with the plastic jacket is the primary concern of the present invention. In addition, however, the backing rollers and/or the intermediate rollers may also be provided with a jacket of plastic, for example, a polyurethane jacket.

Aluminum or aluminum alloys strip is preferably used as the metal strip. However, the present invention also includes the processing of metal strips of other materials, for example, steel strips or stainless steel strips.

The subject matter of the present invention is not only the method described here but also an apparatus for stretch-bend leveling of metal strips. The method described here can preferably be carried out with this apparatus. The apparatus preferably has an inlet tension roller set for establishing the strip tension and an outlet tension roller set for releasing the strip tension. A plurality of stretching rollers, preferably supported individually, is provided between the inlet tension roller set and the outlet tension roller set, the strip being bent around each roller in alternation, increasing the stretching rate. One or more or all of these stretching rollers are provided with a nonmetallic jacket, i.e. a jacket, on the roller outer surface. According to the invention, this jacket is made of plastic, for example, polyurethane. Specifically, reference is made to the discussion of the method described here for the preferred embodiment of the apparatus.

The present invention is described in greater detail below with reference to a drawing showing a single embodiment. In the drawing:

FIG. 1 is a simplified view of an installation for stretch-bend leveling metal strip in a simplified diagram,

FIGS. 2a and 2b are large-scale views of a detail of the system of to FIG. 1 in various embodiments according to the invention, and

FIGS. 3a, 3b and 3c show additional embodiments of the invention.

The drawing shows an apparatus for stretch-bend leveling a metal strip B. The metal strip B may be, for example, an aluminum strip. However, the invention also comprises stretch-bend leveling of strips of steel or of other metals or alloys.

In its basic design, the apparatus has an inlet tension roller set E for setting the strip tension and an outlet tension roller set A for releasing the strip tension. A plurality of stretching rollers 1, 2, 3, 4, 5, about which the strip is bent in alternation to increase the stretching rate is provided between the inlet tension roller set E and the outlet tension roller set A.

Moreover, a deflecting roller U is arranged upstream from the first stretching roller 1. Another deflecting roller may be arranged downstream from the last stretching roller.

Each of these stretching rollers 1 to 5 is supported individually, namely on at least two backing rollers 6 that are not shown in FIG. 1. They may be continuous backing rollers or rows of backing roller segments. At any rate the stretching rollers 1 to 5 are supported individually, i.e. they are not connected to one another in a friction-locking manner by the backing rollers 6 (in contrast with a multiroller leveling unit).

A stretching rate of at least 0.2% is achieved with the stretching rollers 1 to 5. Tensile stress in the metal strip B is created during the stretch-bend leveling process with the inlet tension roller set E and the outlet tension roller set A. The tensile stress amounts to at least 15% of the yield strength of the metal strip, preferably at least 20%.

In the embodiment illustrated here, all stretching rollers 1 to 5 are provided with a nonmetallic jacket 8. Consequently, the individual stretching rollers consist of a roller core 7 and a jacket 8. According to the invention, the jacket is a coating of plastic, preferably polyurethane or a comparable plastic. This jacket 8 may be 1 mm to 10 mm thick, preferably 3 mm to 7 mm thick. The stretching rollers 1 to 5 have a diameter of 25 mm to 100 mm, for example, 35 mm to 70 mm, and the diameter of the stretching rollers is understood not to include the jacket and consequently this is the diameter of the roller core 7.

FIGS. 2a and 2b show embodiments in which only the stretching rollers 1 to 5 are provided with the plastic jacket 8 according to the invention, while the backing rollers 6 and the intermediate rollers 6′ that are optionally provided do not have a jacket. FIG. 2a shows an embodiment with two backing rollers 6, and FIG. 2b shows an embodiment in which intermediate rollers 6′ are additionally provided.

Against this background, FIGS. 3a, 3b and 3c show embodiments in which the additional rollers are provided with a jacket in addition to the stretching rollers 1 to 5.

FIG. 3a shows an embodiment in which the coated stretching rollers 1-5 are each supported on two coated backing rollers 6. The jackets 8′ on the backing rollers 6 may also consist of polyurethane or some other plastic.

FIG. 3b shows an embodiment in which the stretching rollers 1 to 5 are supported by two intermediate rollers 6′ and three backing rollers 6 and/or three rows of segmented backing rollers. In this embodiment, the stretching rollers 1 to 5 and the backing rollers 6 are each provided with a jacket 8 or 8′, while the intermediate rollers 6′ are not coated.

FIG. 3c shows a modification of the embodiment according to FIG. 3b , and the intermediate rollers 6′ here are also provided with a jacket 8″.

Metal strips B can be leveled in a dry operation with the stretch-bend leveling system shown here. In other words, no liquid is sprayed onto the stretching rollers 1 to 5. 

1. A method of stretch-bend leveling metal strip, the method comprising the steps of: bending the metal strip alternately around a plurality of stretching rollers under a tensile stress, and increasing the stretching rate in a downstream strip-travel direction, providing one or more stretching rollers with a plastic jacket.
 2. The method according to claim 1, further comprising the steps of: passing the metal strip through an inlet tension roller set for establishing tension and through an outlet tension roller set for dissipating the tension, the strip is bent alternately around the stretching rollers between the inlet tension roller set and the outset roller set, and the stretching rate of the strip being increased in the strip-travel direction.
 3. The method according to claim 1 wherein each of the stretching rollers is provided with a respective jacket of plastic.
 4. The method according to claim 1, wherein the jacket consists of polyurethane.
 5. The method according to claim 1, wherein the jacket has a Shore A hardness of at least
 90. 6. The method according to claim 1, wherein the metal strip passes through the stretching rollers in dry operation without any spray medium or the like being sprayed onto the stretching rollers.
 7. The method according to claim 1, wherein an angle of wrap around the stretching rollers is adjusted as a function of strip tension so that a maximum linear load applied to the jacket is not exceeded.
 8. The method according to claim 1, wherein a stretching rate of at least 0.2% is produced by the stretching rollers.
 9. The method according to claim 1, wherein the strip is under a tensile stress of at least 15% of the yield point of the metal strip.
 10. The method according to claim 1, wherein the jacket is at least 1 mm thick.
 11. The method according to claim 1, wherein the stretching rollers each have a diameter of 25 mm to 100 mm.
 12. The method according to claim 1, further comprising the step of: supporting each of the stretch rollers individually.
 13. The method according to claim 1, further comprising the step of: adjusting one or more or all of the stretching rollers individually.
 14. The method according to claim 1, wherein three to five stretching rollers are provided between the inlet tension roller set and the outlet tension roller set.
 15. The method according to claim 1, further comprising the step of: supporting the stretching rollers are each supported individually on at least two backing or intermediate rollers.
 16. The method according to claim 15, further comprising the step of: providing the backing rollers or the intermediate rollers also provided with a jacket of plastic.
 17. An apparatus for stretch-bend leveling metal strip the apparatus comprising: an inlet tension roller set for establishing strip tension, an outlet tension roller set for releasing the strip tension, a plurality of stretching rollers between the inlet tension roller set and the outlet tension roller set, the to strip being bent in alternation around the stretching rollers with an increase in the stretching rate, a plastic jacket on one or more stretching rollers.
 18. The apparatus according to claim 17, wherein the jacket is of polyurethane
 19. The method according to claim 1, wherein the jacket is 3 mm to 7 mm thick. 